1. Field of the Invention
This invention relates to a microwave plasma processing method and apparatus.
2. Description of the Prior Art
Conventional microwave plasma processing apparatuses are not free from the problem in that it is difficult to process uniformity a sample because non-uniformity of a microwave electromagnetic field intensity occurs in a reaction chamber due to a waveguide of a fixed shape or the like, or depending on the mode of microwave.
To solve the problem described above, Japanese Patent Laid-Open No. 40380/1987, for example, proposes a method which disposes microwave disturbance means such as a fan having the function of changing the relation between the electromagnetic field of microwave and a substrate inside a reaction chamber, makes uniform the integration, with respect to time, of the electromagnetic field intensity distribution of the microwave ejected into the reaction chamber and forms a uniform and homogeneous deposition film on the entire surface of the substrate. Japanese Patent Laid-Open No. 107538/1989 can be mentioned as a prior art reference of an equivalent type.
In a microwave plasma apparatus equipped with a magnetic field generation coil around the outer periphery of a discharge chamber. Japanese Patent Publication No. 53920/1987 discloses an apparatus which includes mode conversion means for converting the microwave to a circular polarization mode at an intermediate part of a waveguide, rotates a microwave electric field so as to make uniform the electric field intensity as well as the plasma density, and executes uniform etching and CVD. Japanese Patent Laid-Open No. 179323/1989 can be mentioned as a prior art reference of an equivalent type.
The prior art techniques described above make uniform time-wise the non-uniform distribution of the electric field intensity of the microwave and attempts to conduct uniform processing of a sample. Non-uniformity of the electric field intensity of the microwave results from the shape of the waveguide and from the electric field mode but the inventors of the present invention have found a new fact. The experiments carried out by the present inventors demonstrate clearly that the microwave introduced into a discharge tube to generate plasma is reflected by a plasma region or a sample table, this reflected microwave is reflected in a complicated manner in the waveguide and is incident once again into the plasma generation region to generate a high plasma density at part of the region. If such disturbance of the spatial distribution of the plasma density exists, there occurs the problem that the sample cannot be processed uniformly.
Japanese Patent Laid-Open No. 256433/1987 and Japanese Patent Laid-Open No. 145814/1989 can be cited as the prior art references associated with the present invention. Both of these prior art inventions prevent adhesion and deposition of reaction products by heating a discharge tube and an insulating container that define a processing chamber. The former disposes a microwave absorber below a sample position outside the discharge tube and the latter disposes a conductive thin film, to which electric power can be supplied, in the insulating container.